#define I2C_ADDR 0x27 // Define I2C Address where the PCF8574A is
Where did this information come from?
According to the datasheet that I found the possible addresses are as follows:
PCF8574 0 1 0 0 A2 A1 A0 or addresses 0x20 through 0x27
PCF8574A 0 1 1 1 A2 A1 A0 or addresses 0x38 through 0x3F
With the three address lines tied high this would give:
PCF8574 0 1 0 0 1 1 1 or address 0x27
PCF8574A 0 1 1 1 1 1 1 or address 0x3F
So when the documentation was written they used a PCF8574 and when the board was stuffed they used a PCF8574A.
Don